Airpods Pro connected but no sound

I have used airpods pro for like more than 3 months. There has been no problem except the problem with the sound. The airpods are connected but when I play something, the sound comes out of the macbook pro's speaker. So, I go into system preferences, sound, output, it is set to macbook speaker. Ok, so I change it to airpods, then it just changes itself back to macbook speaker. It happened before and it just worked but now it is going very long like 3 weeks. I am so frustrated.